1. Field of the Invention
The present invention relates to a defect analysis method, and more particularly, to a defect analysis method of utilizing at least one nondestructive micro-protection for semiconductor dies or other substrates.
2. Description of the Prior Art
In the semiconductor fabricating process, some small particles and defects are unavoidable. As the size of devices shrinks and the integration of circuits increases gradually, those small particles or defects affect the property of the integrated circuits more seriously. In order to improve the reliability of semiconductor devices, a plurality of tests and monitors is performed continuously to find the root cause of the defects or particles. Then, process parameters can be tuned correspondingly to reduce a presence of defects or particles so as to improve the yield and reliability of the semiconductor fabricating process.
In recent years, the development and usage of focused ion beam (FIB) microscopes have become increasingly popular. By utilizing an ion beam as the emitting source, the FIB microscope is able to perform various analyses or circuit edits on different materials. The structure of a standard FIB microscope is nevertheless complex, including components such as liquid metal ion source (LMIS), electro-lens, scanning electrodes, secondary particle detector, specimen base capable of axial movements, vacuum system, and anti-vibration and anti-magnetic field devices. In general, when an electric field is applied to a liquid metal ion source such as liquid gallium (Ga), the liquid gallium is transformed into a shape with a tiny pointy tip, and by utilizing a negative electric field, the gallium ion can be extracted from the pointy tip.
After being focused by the electro-lens and a series of aperture size alterations, the size of the ion source is confirmed, and after passing the ion beam to the surface of the specimen via a second focusing, the ion beam is able to perform operations including incision and drilling. Having numerous advantages including a low melting point, a low vaporizing pressure, and strong anti-oxidizing capability, gallium has been a popular liquid metal ion source in various commercial systems. Moreover, due to the development of FIB microscopes, semiconductor industries are able to fabricate precise scanning electron microscope (SEM) cross-sectional specimens or transmission electron microscope (TEM) cross-sectional specimens to perform micro-area analyses.
In addition to the fabrication of cross-section specimens provided by transmission electron microscopes, the FIB microscopes provide an alternative specimen fabrication tool for the users, in that the FIB microscopes are capable of achieving a success rate of greater than 90% within a working hour between 2–6 hours, and by utilizing the specimens fabricated by the FIB microscopes, the transmission electron microscopes are able to obtain satisfactory resolution and contrast results. However, when the ions collide with the specimens, phenomena such as gasification and ionization will occur on the surface of the specimen, neutral atoms, ions, and electrons will be produced, and a small quantity of the ions will be implanted into the specimen. The implanted ions are all destructive in nature and when these focused ion beams are utilized to fabricate cross-sectional specimens from a defect located on the surface of a wafer, the defect or the surface of the wafer will be damaged. In mild cases, an amorphous layer containing the ion source element (gallium in general) will form over the surface of the specimen, whereas in severe cases, precipitate containing the ion source element will be generated. At any rate, either case will damage the specimen and influence the result of the observation. When the defect is not located on the surface layer of the specimen, a layer disposed on the defect will be first removed to expose the defect. Next, a scanning electron microscope or an optical microscope is used to perform a top-view observation on the defect and a focused ion beam is used to fabricate a cross-sectional specimen. In either condition, the chance of damaging the defect remains the same.
Recently, a new type of FIB microscope referred to as the dual beam system has been introduced. Capable of providing two particle beams (ion beam plus electron beam) simultaneously, the electron beam of the dual beam system can be utilized to form a platinum (Pt) protective layer over the surface of the defect. Despite having several advantages, the dual beam system still remains unpopular as a result of an overly high cost and other problems caused during fabrication of cross-section specimens. Please refer to FIG. 1. FIG. 1 is a perspective diagram showing the method of fabricating a TEM cross-section specimen 10 by using a FIB microscope of a dual beam system according to the prior art. (As shown in FIG. 1, the TEM cross-section specimen 10 comprises a plurality of trenches 12 thereon and when the trenches 12 are not filled with stuffing materials, the platinum layer formed by evaporation process will not only cover a defect 14, but also will fill the trenches 12 (both not shown in the figure). Since the high atomic number and electron scattering of the platinum layer is much stronger, the electrons are not likely to penetrate the layer and black areas will be produced as a result of contrast difference, thereby blocking the defect 14 and increasing the difficulty of observation.
Additionally, a conventional method of utilizing transparent resin or glue to cover the specimen entirely has also been introduced. Despite the fact that this method is effective for increasing the contrast between the protective layer and the surface layer structure, it is unfortunately ineffective for searching and confirming the exact location of the defect by utilizing the FIB microscope. Because the electrical conductivity of the protective layer produced by the method is poor, thereby resulting in electron charging. As the electron charging occurs, the precise location of the defect will be difficult to determine.
Hence it remains a challenge to provide a default analysis method that is not only able to provide a protective layer for the defect while the focused ion beam is utilized for fabricating a specimen, but that can also accurately determine the location of the defect and perform necessary observations by preventing the blocking of the defect and the electron charging.